The invention relates to ultrasonic measuring systems and especially those that utilize an ultrasonic transducer for sending and receiving ultrasonic signals that are directed through a volume of liquid in a container to measure the level of the liquid. More particularly, the invention relates to a probe or stillwell in the form of a tube located in the volume of liquid with its axis generally perpendicular to the surface of the contained liquid.
Ultrasonic measuring systems are commonly used to measure the level of liquid in containers such as fixed storage tanks, fuel storage reservoirs and aircraft fuel tanks. These systems generally use a tubular probe or stillwell inserted approximately vertically in the tank. An ultrasonic transducer transmits a sinusoidal acoustical pulse through the stillwell to the surface of the liquid. Then an echo returns from the surface of the liquid to the transducer and provides a sinusoidal echo signal. A receiver responds to the echo signal and the total elapsed time is determined. Thus, further data is calculated for display.
In these systems, a transducer assembly containing a piezoelectric crystal is usually connected to the stillwell at or near the bottom of the tank. The stillwell generally has openings through its tubular wall near the bottom of the tank to admit liquid from the surrounding volume. The tube is usually open at the top so that the height of the column of liquid in the tube is essentially the same as the height of the contained liquid volume.
In order to assure accurate measurements, it is desirable to provide baffles around the lower end portion of the tube or probe to prevent the entrance of air bubbles into the liquid filled column. The presence of bubbles in the column through which the ultrasonic pulse is directed could adversely effect the resulting measurement.
The bubble baffles typically are constructed of concentric sleeves with offset, interconnecting holes for fluid passage so that the liquid can have access to the interior of the tube. The bubbles are apt to be generated particularly in aircraft fuel tanks due to sudden movements and changes in attitude of the aircraft. Also, bubbles may be generated during refueling.
Some ultrasonic fuel measurement systems may require the determination of the fuel dielectric constant in order to calculate the density of the liquid. It is important to calculate fuel density on a continuous basis due to variations thereof that occur in response to temperature changes, changes in the velocity of sound and in the dielectric constant. Accordingly, these particular systems must utilize an electrical device or sensor to determine the dielectric constant.
Such dielectric sensors are typically constructed of a number of concentric sleeves emersed in the liquid. The sleeves are formed of an electrically conductive material and are adapted to function as the plates of a capacitor. By determining the electrical capacitance between the opposed surfaces of the emersed concentric tubes, the dielectric constant can be calculated.
It will be seen that these requirements, among others, dictate that a rather complex assembly be provided in order to properly utilize the stillwell or probe to obtain the fuel level measurements sought.
The baffle assembly of the present assembly reduces the difficulties described above and affords other features and advantages heretofore not obtainable.